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                Never Wait for Weights                </h1>
                <p>时间限制：15s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div>在实验室中，Nathan Wada作为助手的职责是测定两个样品的重量差异。当样品的差异很小时，使用天平能比使用</div>
<div>弹簧秤得到更精确的结果，所以他只使用天平来测得一些样品的重量差。他偶尔会被询问一些样品的重量差，而他</div>
<div>能否回答这些问题取决于在回答相应问题时他已经得到的测量结果。由于他所在处理的测量数据是巨大的，所以他</div>
<div>希望你能写个程序帮他处理数据和回答问题。</div>
<p></p></p><hr/><h3>输入格式</h3><p><div>输入包含多组测试数据。每组数据第一行包含两个整数 N 和 M ，其中 N 表示样品的数量，</div>
<div>样品从 1 到 N 标号，满足 2&le;N&le;100000 。</div>
<div>接下来 M 行，每行包括一个测量结果或者询问，按时间顺序给出，满足 1&le;M&le;100000 。</div>
<div>一个测量结果被格式化为 ! a b w ，表示第 a 个样品比第 b 个样品轻 w 个单位重量</div>
<div>满足 a&ne;b,0&le;w&le;1000000 ，且任意的测试结果互不矛盾。</div>
<div>一个询问被格式化为 ? a b ，表示询问第 a 个样品比第 b 个样品轻多少个单位重量，满足 a&ne;b 。</div>
<div>输入以两个零作为结束。</div>
<p></p></p><hr/><h3>输出格式</h3><p><div>对于每个询问输出一行，如果能回答问题，则输出问题的答案，你可以认为答案的绝对值不超过 1000000&nbsp;</div>
<div>否则输出 UNKNOWN ，表示不能回答问题。</div>
<p></p></p><hr/><h3>样例输入</h3><pre>2 2
! 1 2 1
? 1 2
2 2
! 1 2 1
? 2 1
4 7
! 1 2 100
? 2 3
! 2 3 100
? 2 3
? 1 3
! 4 3 150
? 4 1
0 0 </pre><hr/><h3>样例输出</h3><pre>1
-1
UNKNOWN
100
200
-50</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>鸣谢Tangjz提供试题</p>
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